Is cavity wall insulation right for me?
Guide to Wall Insulation
Up to half of the heat loss from a house occurs through the walls. This can be reduced by two-thirds by insulating the walls.
Most houses built before about 1980 have no wall insulation. Many (though not all) houses built during the 1980s have some wall insulation. Houses built since the 1991 Building Regulations came into effect are required to have wall insulation.
Insulation may be placed on the outside, in the cavity or on the inside of a wall, without altering the overall insulation properties.
When considering wall insulation, first you should find out whether your house has cavity walls or solid walls. A building contractor, BER Assessor or architect will be able to tell you if you have cavity walls in your new or older house.
Cavity wall insulation
The walls of many houses consist of two ‘leaves’ of brick or concrete block with a cavity or space between them to resist rain penetration.
In older houses insulation can be injected into this cavity through holes drilled through the outer leaf, by means of a blowing or pumping machine.
Since the work is done from outside, it cause minimum disturbances inside. The drilled holes, which are typically about 25mm (1 inch) in diameter and spaced a metre or so apart, are then filled to match the wall appearance as closely as possible. The job typically takes less than a day.
In relation to the pumping of your walls with a bonded bead system you would noticeably improve the overall thermal properties of your house and in turn reduce your energy bills for the winter months.
Suitability of Cavity Insulation
It is important before deciding to insulate existing cavity walls that you check their suitability for cavity insulation. This assessment will take account of the degree of exposure of the house to wind-driven rain and the construction details and condition of the walls. Any ventilation openings in the wall will also be checked to ensure that these will not be blocked by the insulation.
There are a number of issues you should be aware when filling your wall’s cavity:
If there were any frost or structural damage to any of the house’s external walls pumping of beads into the cavity would not be advised.
The width of the cavity between your external wall leaf and the installed aero-board should be at least 50mm.
If there is any problem with dampness in the internal leaf it would not be recommended to add the beads to the cavity as they would only increase the path for water to travel into the wall.
If the wall suffers from rain penetration at times, this problem must be remedied first.
In some cases, the walls may be found to be unsuitable for cavity insulation or may require some remedial work beforehand.
The cost of cavity wall insulation depends on a number of factors, including the width of the cavity, but it is typically in the region of €5 to €7 per square metre. For a typical semi-detached house, this gives a total cost of about €550-€700. With annual fuel savings of €200 to €320, the payback period will be in the region of 4 to 7 years.
You may be able to negotiate a lower price if you can persuade some of your neighbours to have their walls insulated at the same time.